The answer to your question will depend on how your organisation defines value.
Value isn't just about changes to revenue/profit. There are many forms of value, such as:
The cost associated with not making a change
The value of removing or lowering a risk
A strategic decision
...and many more.
The question then becomes: how do you ...
Calculating ROI for individual investments that don't provide additional benefit but only or mainly prevent loss isn't always meaningful. This becomes apparent if you look at possible combinations of such investments.
If you were required to implement two features A and B to prevent a loss of $1M, is each feature's ROI $500,000 or $1M? Both values can't be ...